This invention relates to ultrasound imaging for medical applications and, more particularly, to integrated circuitry including both low and high-voltage components for use with ultrasound transducer elements.
Ultrasound imaging systems for medical applications typically employ arrays of individual ultrasound transducer elements which transmit and receive ultrasound energy. The transducer array transmits ultrasound energy into a region of interest in a patient, and receives reflected ultrasound energy, or echos, from various structures and organs within the patient""s body. The imaging system then processes electronic signals generated by the elements of the transducer array, based on the received ultrasound energy, to form an image of the region of interest. The quality or resolution of the image formed is a function of the number of transmit and receive transducer elements that constitute the transducer array.
Accordingly, to achieve high image quality, a large number of transducer elements is desirable. For both two-dimensional and three-dimensional imaging applications, a preferred number of transducer elements is typically determined by a desired image resolution. The transducer elements typically are located in a hand-held transducer xe2x80x9cheadxe2x80x9d or xe2x80x9chandlexe2x80x9d which is connected by a flexible cable to an electronics unit that processes the transducer signals and generates ultrasound images, as described above. Some proposed transducer heads may also include circuitry to provide transmit signals to, and process receive signals from, the individual transducer elements. Practical considerations of size, cost, and the complexity of this circuitry, as well as practical limits on the size and flexibility of the cable which carries signal conductors connecting the transducer elements to the electronics unit, pose challenges to the design of a transducer head that incorporates a large number of transducer elements for high resolution imaging applications.
In some proposed ultrasound imaging systems, the transmit circuitry that may be included in the transducer head includes high-voltage components to drive the individual ultrasound transducer elements. In some cases, low-voltage high-density digital logic circuitry to provide transmit signals to the high-voltage drivers may also be included in the transducer head. The high-voltage drivers are made from high-voltage components that are capable, for example, of operating voltages of up to approximately 100 volts. The high-voltage drivers may be fabricated as discrete components or as integrated circuits including several drivers. The low-voltage logic circuitry is fabricated as a separate integrated circuit having an operating voltage on the order of 5 volts.
In addition to transmit circuitry including the high-voltage drivers and low-voltage logic circuitry, some proposed transducer heads may include low noise, low-voltage analog receive circuitry. The low-voltage receive circuitry, like the transmit logic circuitry, typically has an operating voltage on the order of 5 volts, and may be a separate integrated circuit or may be fabricated with the low-voltage transmit logic circuitry as a monolithic integrated circuit.
As discussed above, in order to facilitate the use of a large number of transducer elements to achieve high-quality ultrasound images, it is desirable to integrate as much circuitry as possible in as small a volume as possible to reduce the size and complexity of the circuitry, whether the circuitry be located within a transducer head or in an electronics unit separate from the transducer head. In particular, if the circuitry is included in the transducer head, it is desirable to reduce the number of interconnections between any discrete integrated circuits and components within the head, as well as the number of signal conductors in the cable connecting the transducer head to the electronics unit. However, notwithstanding a reduced number of interconnections or signal conductors, the discrete high-voltage components typically employed to drive the transducer elements take up valuable space within the transducer head.
In addition, some applications, for example very high-frequency ultrasound imaging, require that transmit circuitry be located as close as possible to the transducer elements to avoid signal loading by a long cable. Accordingly, it would be advantageous to integrate high-voltage drivers for ultrasound transducer elements with either or both of the low-voltage transmit logic circuitry and the low-voltage receive circuitry as a monolithic integrated circuit.
However, high-voltage devices do not readily lend themselves to fabrication using conventional processing techniques for low-voltage integrated circuits. For example, high-voltage FETS are typically fabricated using relatively large geometry processes (10 microns) to achieve high breakdown voltages. In contrast, low-voltage integrated circuits may be fabricated using submicron geometry processes. The requirement of large junction areas for high-breakdown-voltage components is difficult to achieve using the small-geometry, high-density processing techniques employed in the fabrication of low-voltage integrated circuits. Additionally, high-voltage fabrication processes have the disadvantage that they often do not include the capability of fabricating bipolar junction transistors, which are used in many low-noise signal processing applications.
One proposed application related to actuation of mechanical devices is reported in xe2x80x9cHigh voltage devices and circuits fabricated using foundry CMOS for use with electrostatic MEM actuators,xe2x80x9d N. I. Maluf et al., Sensors and Actuators, vol. A52, pp. 187-192, 1996. In this proposal, high-voltage components and circuits for use with electrostatic micro-electromechanical (MEM) devices are fabricated using conventional processing techniques for high-density, low-voltage integrated circuits. In one example of this application, MEM actuators requiring a high-voltage drive are monolithically integrated on a single substrate with high-voltage components, using low-voltage processing techniques.
For this application, high-voltage MOS transistors are fabricated using a 2.0 micron CMOS process that includes the formation of N-well and P-base layers as lightly doped drains. High-voltage transistors fabricated in this manner are reported to have operating voltages of approximately 100 volts or less for NMOS structures, and approximately xe2x88x9225 volts or less for PMOS structures. However, the use of low-voltage integrated circuit processing techniques for the fabrication of high-voltage components is limited in this application to simple high-voltage differential amplifiers for driving aluminum electrostatic MEM actuator structures.
One possible approach to integrating high and low-voltage circuitry is to design and develop a custom integrated circuit fabrication line dedicated to a hybrid process. Such a hybrid process would require many masks for the various steps necessary to implement both the high and low-voltage components, and would present several optimization challenges. Moreover, designing and implementing a dedicated integrated circuit fabrication line for a custom process would be cost effective only if a large number of the custom integrated circuits are manufactured.
Another proposed solution for optimizing ultrasound imaging systems includes the design of a low-voltage transducer element by using multi-layer ceramics. Such low-voltage transducer elements eliminate the need for high-voltage transducer driver circuitry. However, as in the case of a custom integrated circuit hybrid fabrication process, the multi-layer ceramics used for low-voltage ultrasound transducer elements are costly and difficult to produce.
Accordingly, for ultrasound imaging systems and many other applications, it is desirable to integrate both high and low-voltage circuitry in a monolithically fabricated integrated circuit using readily available and reasonably cost-effective processing techniques. In particular, the integration of high and low-voltage circuitry would provide advantages for ultrasound imaging systems by facilitating the packaging of higher density high and low voltage circuitry, as well as a large number of transducer elements, in the small volume of a transducer head.
In view of the foregoing, the present invention is directed to integrated circuitry including both high and low-voltage components for use with transducer elements of an ultrasound imaging apparatus. According to one embodiment of the invention, the integrated circuitry comprises a low-voltage circuit and a high-voltage circuit including a high-voltage FET to drive an ultrasound transducer element. The low-voltage circuit and the high-voltage circuit are monolithically formed on a single substrate.
In one aspect of the invention, the low-voltage circuit includes conventional low-voltage CMOS circuitry having a CMOS breakdown voltage. The high-voltage FET of the high-voltage circuit includes a lightly doped drain region which is doped such that a drain-substrate breakdown voltage of the high-voltage FET is greater than the CMOS breakdown voltage of the low-voltage circuit. The lightly doped drain region of the high-voltage FET may be a lightly doped n-well or n-base region for an NMOS device, or a lightly doped p-well or p-base region for a PMOS device.
According to another aspect of the invention, the low-voltage circuit of the integrated circuitry includes high-density digital logic circuitry electrically coupled to the high-voltage circuit. The high-density digital logic circuitry may include a digital sequencer. In yet another aspect, the low-voltage circuit includes a low-voltage transmit circuit and a low-voltage receive circuit. In this aspect, the low-voltage transmit circuit includes high-density digital logic circuitry electrically coupled to the high-voltage circuit, and the low-voltage receive circuit includes low noise analog receive circuitry to process a receive signal from the ultrasound transducer element.
According to another aspect of the invention, the high-voltage circuit includes a pull-up circuit electrically coupled between a high voltage and the high-voltage FET. The pull-up circuit may include one or more resistors, bipolar junction transistors, or FETs. Additionally, the pull-up circuit may include a cascoded series configuration of at least two pull-up transistors, electrically coupled to the high voltage and having a pull-up control gate, to output a drive current to the ultrasound transducer element based on a drive signal input to the pull-up control gate. The pull-up circuit may also include a gate drive transistor to receive an input signal from the low-voltage circuit and output the drive signal to the pull-up control gate.
In another example of a pull-up circuit according to one embodiment of the invention, the pull-up circuit includes a pull-up transistor circuit electrically coupled to the high-voltage, comprising at least one pull-up transistor having a pull-up control gate. If the pull-up transistor circuit includes more than one pull-up transistor, each pull-up transistor has a pull-up control gate and is connected in series with another pull-up transistor. The pull-up transistor circuit outputs a drive current to the ultrasound transducer element based on a drive signal input to the pull-up control gate of each pull-up transistor. The pull-up circuit also includes a gate drive transistor for each pull-up transistor, wherein each gate drive transistor receives an input signal from the low-voltage circuit and outputs the drive signal to the pull-up control gate of a respective pull-up transistor.
In another embodiment, the invention includes integrated circuitry for use with ultrasound transducers, comprising a first low-voltage CMOS circuit including high density digital logic circuitry having a CMOS breakdown voltage and a high-voltage CMOS circuit to drive an ultrasound transducer element. The high-voltage CMOS circuit receives an input signal from the first low-voltage CMOS circuit and includes a high-voltage FET. The high-voltage FET includes a lightly doped drain region and has a breakdown voltage greater than the CMOS breakdown voltage. The first low-voltage CMOS circuit and the high-voltage CMOS circuit are monolithically formed on a single substrate.
The integrated circuitry according to this embodiment of the invention may further include a second low-voltage CMOS circuit monolithically formed with the first low-voltage CMOS circuit and the high-voltage CMOS circuit on the single substrate. The second low-voltage CMOS circuit may include low noise analog receive circuitry to process a receive signal from the ultrasound transducer element.
According to yet another embodiment, the invention is directed to an integrated high-voltage driver circuit for use with ultrasound transducers. The integrated high-voltage driver circuit comprises a high-voltage FET driver to drive an ultrasound transducer element, and a pull-up circuit. The pull-up circuit includes a pull-up transistor circuit electrically coupled to a high voltage and having a driver output electrically coupled to one of a source and a drain of the high-voltage FET driver. The pull-up transistor circuit comprises at least one pull-up transistor having a pull-up control gate, and if the pull-up transistor circuit includes more than one pull-up transistor, each pull-up transistor has a pull-up control gate and is connected in series with another pull-up transistor. The pull-up transistor circuit outputs a drive current to the ultrasound transducer element based on a drive signal input to the pull-up control gate of each pull-up transistor. The pull-up circuit also includes a gate drive transistor for each pull-up transistor, wherein each gate drive transducer receives an input signal and outputs the drive signal to the pull-up control gate of a respective pull-up transistor. The high-voltage FET driver and the pull-up circuit are monolithically formed on a single substrate.
In one aspect, the integrated high-voltage driver circuit further includes an inverter to receive the input signal and output a transmit signal to a driver control gate of the high-voltage FET driver. In yet another aspect, the pull-up transistor and the gate drive transistor of the pull-up circuit are high-voltage FETs.
According to yet another aspect of the integrated high-voltage driver circuit, the pull-up transistor of the pull-up circuit includes a plurality of pull-up transistors cascoded in series. The plurality of cascoded pull-up transistors is coupled between the high voltage and either the source or the drain of the high-voltage FET driver. The gate drive transistor may also include a plurality of gate drive transistors, wherein each gate drive transistor outputs a drive signal to one of the plurality of pull-up transistors.
Other advantages, novel features, and objects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.